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A magnetron injection gun operating with temperature limited electron emission has been designed for a gyrotron amplifier. A series of computer models of the gun anode region were used to determine selected thermal and structural characteristics. Their effects on electron beam energy, velocity spread, and temperature were evaluate. The Thermal analysis yielded the steady state temperatures of 137 node points. Thermally induced mechanical expansions were found to be 0.20% axially and 0.82% radially. In the three dimensional coordinate sytem utilized, the stress in 373 elements were numerically evaluated. The cathode heater power brought the cathode emitter up to 1068°C in 500 seconds. The cathode cooling due to electron emission was found to increase the steady state heater input power requirement by 11% (for an emitter temperature of 1068°C) from 9 W to 11 W. The electron trajectory analysis included an evaluation of the beam energy, velocity spread, and temperature. The effect of the deformed mechanical shapes on the beam paremeters was determined. A two dimentional computer simulation was used to graphically depict the electron trajectories in the gun anode region.